Aspidogastrea

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Introduction

The Aspidogastrea is a small group of flukes comprising about 80 species. It belongs to the Trematoda, which comprises the two subclasses Aspidogastrea and Digenea. Species range in length from approximately one mm to several cm. They are parasites of freshwater and marine molluscs and vertebrates (cartilaginous and bony fishes and turtles). Maturation may occur in the mollusc or vertebrate host. None of the species has any economic importance, but the group is of very great interest to biologists because it has several characters which appear to be archaic. For example, the hosts
of aspidogastreans include chondrichthyan fishes (sharks, rays and chimaeras), a group that is 450 million years old, whereas the sister group of the aspidogastreans, the digeneans, are known from teleost fishes (210 million years old) as well as from various "higher" vertebrates; very few species have invaded chondrichthyans secondarily.

Aspidogastreans have a nervous system of extraordinary complexity, greater than that of related free-living forms, and - likewise - they have a very great number of sensory receptors of many different types. Their life cycle is much simpler than that of digenean trematodes, including a mollusc and a facultative or compulsory vertebrate host. There are no multiplicative larval stages in the mollusc host, as known from all digenean trematodes. Furthermore, host specificity of most aspidogastreans is very
low, i.e., they infect a wide range of hosts, whereas a typical digenean trematode is restricted to few species (at least of molluscs). Aspidogastreans may survive for many days or even weeks outside a host in simple media (water, saline solution). All this has
led to the suggestions that aspidogastreans are archaic trematodes, not yet well adapted to specific hosts, which have given rise to the more "advanced" digenean trematodes, and that the complex life cycles of digenean trematodes have evolved from
the simple ones of aspidogastreans (Rohde, 1972, further references therein).

Characteristics

Shared characteristics of the group are a large ventral disc with a large number of small alveoli (suckerlets) (Fig. 1, see also
Structure of the juvenile and adult)
or a row of suckers and a tegument with short protrusions, so-called microtubercles.

The Families of the Aspidogastrea

Gibson (1987) and Rohde (2001) distinguish four families of Aspidogastrea:

The Rugogastridae include a single genus, Rugogaster, with two species from the rectal glands of holocephalan fishes. It is characterised by a single row of rugae (transverse thickenings of the tegument) developing from the posterior wall of the anteriorly located ventral sucker, numerous testes, and two caeca. Species of all other families have a single caecum and either one or two testes.

The Stichocotylidae include the single species Stichocotyle nephropis from the intestine of elasmobranchs. It has a single ventral row of well separated suckers.

The Multicalycidae include the single genus Multicalyx from the intestine of holocephalans and elasmobranchs. It is characterised by a single ventral row of alveoli separated by transverse septa.

The Aspidogastridae includes species infecting molluscs, teleosts and turtles. The ventral adhesive disc bears either three or four rows of alveoli. Rohde distinguishes three subfamilies of Aspidogastridae, the Rohdellinae, Cotylaspidinae and Aspidogastrinae. The first subfamily includes the single species Rohdella siamensis from freshwater teleosts; the terminal male and female genital ducts are united to form a hermaphroditic duct, which is absent in the other two subfamilies. The Cotylaspidinae have an adhesive disc bearing three, and the Aspidogastrinae have an adhesive disc bearing four longitudinal rows of alveoli. The genera Cotylogaster, Cotylaspis and Lissemysia of the Cotylaspidinae differ in the absence or presence of a cirrus pouch and the number of testes (one or two), the genera Multicotyle, Lobatostoma, Aspidogaster, Lophotaspis, Sychnocotyle, and Neosychnocotyle of the Aspidogastrinae also differ in the number of testes (one or two), the absence or presence of a cirrus pouch, and - in addition - in the absence or presence of head lobes and/or papillae on the adhesive disc.

Discussion of Phylogenetic Relationships

The tree presented here is a preliminary one and must be confirmed by DNA
studies. It shows four families, the Aspidogastridae infecting teleosts and
turtles, and the Stichocotylidae, Multicalycidae and Rugogastridae
infecting chondrichthyans (holocephalans and elasmobranchs). A synapomorphy
for all Aspidogastrea is the presence of an adhesive disc, a synapomorphy
of the Aspidogastridae is an adhesive disc which is subdivided into three
or four rows of alveoli, a synapomorphy of the other three families is an
adhesive disc consisting of a single longitudinal row of suckers, rugae or
deep alveoli. An adhesive disc consisting of a row of suckers is apomorphic
for the Stichocotylidae, an adhesive disc consisting of a single row of
deep alveoli is apomorphic for the Multicalycidae, and an adhesive disc
consisting of rugae is apomorphic for the Rugogastridae. The plesiomorphic state within the Aspidogastrea is likely to be a posterior, undivided sucker as found in larval aspidogastreans and
digeneans.

The four families of aspidogastreans are also recognized by Gibson (1987) and Rohde (2001). Gibson (1987, also Gibson and Chinabut 1984) further recognized two
orders, the Aspidogastrida with the single family Aspidogastridae, and the
Stichocotylida including the Stichocotylidae, Multicalycidae and
Rugogastridae. However, similarities between species of these two orders
are so great that distinction at the level of orders does not seem
justified.

The sister group of the Aspidogastrea is the Digenea, both comprising the
Trematoda. Synapomorphies of the trematodes are presence of a Laurer's
canal, a posterior sucker (transformed to an adhesive disc in the
Aspidogastrea), and life cycles involving molluscs and vertebrates. DNA
studies have consistently supported this sister group relationship. The
question of whether vertebrates or molluscs are the original hosts of the
trematodes, has not been resolved (see discussion in Rohde 2001).

Littlewood, D.T.J., Rohde, K. and Clough, K.A. (1999). The interrelationships of all major groups of Platyhelminthes: phylogenetic evidence from morphology and molecules. Biological Journal of the Linnean Society 66, 75-114.

Littlewood, D.T.J., Rohde, K., Bray, R.A. and Herniou, E.A.(1999). Phylogeny of the Platyhelmimthes and the evolution of parasitism. Biological Journal of the Linnean Society 68. 257-287.

Rohde, K. (1994b). The origins of parasitism in the Platyhelminthes. International Journal for Parasitology 24, 1099 - 1115.

Rohde, K. (2001). The Aspidogastrea, an archaic group of Platyhelminthes.In: Interrelationships of the Platyhelminthes, pp. 159-167 (eds. Littlewood, D.T.J. and Bray, R.A.). Taylor and Francis, London and New York.

Amato, J.F.R. and Pereira, J.Jr. (1995). A new species of Rugogaster (Aspidobothrea: Rugogastridae) parasite of the elephant fish, Callorhinchus callorhinchi (Callorhinchidae), from the estuary of the la Plata river, coasts of Uruguay and Argentina. Revista Brasiliera de Parasitologia Veterinaria 4, 1- 7.

Blair, D. (in press). Parasitic flatworms and the phylogenetic position of the Aspidobothrea inferred from DNA sequence data. International Journal for Parasitology

Bray, R. A. (1984). Some helminth parasites of marine fishes and cephalopods of South Africa: Aspidogastrea and the digenean families Bucephalidae, Haplosplanchnidae, Mesometridae and Fellodistomidae. Journal of Natural History 18, 271-292.

Dandotia, M. R. and Bhadauria, S. (1977). Trematode parasites of fresh water fishes of Gwalior: a new species of the genus Aspidogaster Baer, 1827. All-India Symposium on helminthology, Srinagar, Kashmir, 12.

Hathaway, R. P. (1972a). Some observations on the ultrastructure of the female reproductive system of Aspidogaster conchicola (Trematoda: Aspidobothria). Journal of the Colorado-Wyoming Academy of Science 7, 114.

Hendrix, S. S., Vidrine, M. F. and Hartenstine, R. H. (1985). A list of records of freshwater aspidogastrids (Trematoda) and their hosts in North America. Proceedings of the Helminthological Society of Washington 52, 289-296.

Justine, J.L. (1997). The general classification of parasitic Platyhelminthes: recent changes, and the use of ultrastructural characters, particularly those of spermatozoa. Bulletin Soc. zool. France 122, 269-277.

Justine, J.L. (1998). Non-monophyly of the monogeneans? International Journal for Parasitology 28, 1653-1657.

Littlewood, D.T.J., Rohde, K., Bray, R.A. and Herniou, E.A.(1999). Phylogeny of the Platyhelmimthes and the evolution of parasitism. Biological Journal of the Linnean Society 68. 257-287.

Littlewood, D.T.J., Rohde, K. and Clough, K.A. (1999). The interrelationships of all major groups of Platyhelminthes: phylogenetic evidence from morphology and molecules. Biological Journal of the Linnean Society 66, 75-114.

Rohde, K. (2001). The Aspidogastrea, an archaic group of Platyhelminthes.In: Interrelationships of the Platyhelminthes, pp. 159-167 (eds. Littlewood, D.T.J. and Bray, R.A.). Taylor and Francis, London and New York.

Thoney, D. A. and Burreson, E. M. (1987). Morphology and development of the adult and cotylocidium of Multicalyx cristata (Aspidocotylea), a gall bladder parasite of elasmobranchs. Proceedings of the Helminthological Society of Washington 54, 96-104.

Page: Tree of Life
Aspidogastrea.
Authored by
Klaus Rohde.
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First online 22 September 1998

Content changed 24 September 2008

Citing this page:

Rohde, Klaus.
2008. Aspidogastrea.
Version 24 September 2008. http://tolweb.org/Aspidogastrea/20399/2008.09.24in The Tree of Life Web Project, http://tolweb.org/

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